NASA Titan moon-balloons to run on cloud fuel

Boffins are working on a cunning new plan to power future hot-air-balloon probe craft sent to survey Titan, ice moon of Saturn. The balloons' burners will be fuelled by the evaporated patio gas which occurs naturally in the Titanian atmosphere.

Flying over a mountain made of ice in a cloud-burning balloon.

The faraway moon, orbiting its colossal, ringed motherworld, is one of the most intriguing places known to humanity. Despite the fact that it is relatively small it has a denser atmosphere than Earth, and like Earth - and no other known body - it has large bodies of liquid on its surface.

These bodies of liquid aren't water, however. Far from the sun in the outer solar system, prevailing temperatures on Titan are around -180°C. Water there behaves more like rock. Its place is taken by hydrocarbons such as methane, ethane and so on, what we find in our patio-gas cylinders here on Earth. These chemicals are mainly liquid at Titanian temperatures, as water is here; but just as we have water clouds and rain, so too does Titan have patio-gas clouds and rain. Titanian "air" is thought by NASA boffins to be roughly 4 per cent of methane by volume, the rest being almost all nitrogen.

The lack of any free oxygen in the ice-moon's air means that the patio gas oceans, clouds etc won't normally catch fire. Thus NASA's plan for Titanian hot-air ballooning would reverse the situation on Earth: Rather than burning a stream of patio-gas using oxygen in the air, the moon balloons will burn a stream of oxygen using methane from the surrounding clouds.

The original NASA balloons-above-Titan plans had intended to warm the air in the lifting envelope using only waste heat from the radioisotope power unit provided to run the probe's systems. (Solar power is useless on Titan as the sun is very far away and anyway veiled by the thick atmosphere.) This should work most of the time, as the dense atmosphere and low gravity will mean that a balloon performs far better than it would on Earth. (It has been calculated that humans on Titan would be able to fly using strap-on wings due to the same factors.)

Nonetheless, boffins at NASA's Jet Propulsion Laboratory are concerned that a radioisotopic-heat-only balloon, unable to adjust height at all quickly, might crash haplessly into one of Titan's icy mountains. Hence the plan for an oxygen-fuelled rapid buoyancy modulation system (BMS).

“We believe that an air-breathing system is key to providing extended mission duration and a lightweight and low volume solution,” says Dr James Sisco, lead brainbox on the BMS. “This technology could be a key enabler for future balloon missions to Titan.”

With only 4 per cent of the atmosphere being good, burny stuff - as opposed to 20 per cent here on Earth - designers believe that a pilot flame will be needed to keep the main burner burning. This is to come from a "catalytic reactor" provided by famous crazytech firm Aurora Flight Sciences.

There are other radical schemes for Titanian exploration in the works, perhaps most notably the plan for a small robotic sailing boat to cruise the freezing LPG seas of the moon's arctic regions - the excellently named "Sea of Krakens", perhaps - whose existence was recently confirmed beyond all doubt by a glint of sunlight snapped by the Cassini probe in orbit about Saturn.

What with all the cunning exploration plans and interesting revelations of Earth-like liquid driven topology, weather etc, Titan surely has to be one of the most interesting places in the solar system these days. ®